If the blob column is not storing the data in Pega proprietary format, then you can't use Pega user defined functions to read that probably. You might need to use Oracle functions to read the blob in a query called from Pega; use RDB methods. Once you have the data available with you, you need to open the data in a file and for that sendFile api method is available. You may need to do some typecasting of the data before passing that to sendFile method.